The present invention relates to a hydraulic control device having a directional valve by which the direction of movement and the speed of a hydraulic consumer, especially a mobile working device, can be modified. Such a hydraulic control device is known from actual use on excavators.
Mobile working machines such as, in particular, wheel excavators or wheel loaders frequently operate without support. Under these circumstances the entire vehicle can be incited to oscillation upon rapid actuation of a working function, these oscillations then being propagated via the cab to the driver. If the oscillating circuit is closed over the operating element of the pre-control device, the operating movement is unstable and can no longer be controlled. A sudden transition to large control signals namely brings about large forces of acceleration so that strong oscillations can be excited. Furthermore, the control slide of the directional valve is then in a steeply ascending region of the characteristic curve of the directional valve and thus in the region of high amplification, so that the tendency to oscillate is further promoted.
In order to dampen the oscillations it is known to install valve arrangement developed as throttle non-return valves in the control lines to the control slide of the directional valve. Good damping action would be obtained if the damping cross section were selected very small. In that way, however, the course of the movement is delayed. A delaying of the start of the movement is annoying for the part of the operator and leads to the danger of overcontrol. A delay in the end of the movement results in an "overrunning" of the working device, which makes precise work difficult and furthermore represents a safety risk. For these reasons, only slight damping is used in the known control devices, which, however, does not reduce the susceptibility to oscillation of the entire system to the extent desired.